1. Field of the Invention
This invention relates to a method of forming toothed belts/belt sleeves which have a cloth layer disposed on a surface thereof. The invention is also directed to a belt/belt sleeve made according to the inventive method.
2. Background Art
Conventional toothed belts have a body with an inside and an outside. Teeth are formed on the inside of the body and are commonly made from chloroprene rubber. Load carrying cords, which are embedded in the body, are made from glass fiber cord or aramid fiber cord, commonly processed with an adhesive resorcinol-formalin-latex (RFL) liquid with an SBR-based vinylpyridine latex component. A cover canvas having crimped nylon in the weft yarns covers the teeth. This type of belt is commonly used as an overhead cam (OHC) driving belt for automobiles.
The cover canvas typically has a joint with free edges which are joined through either a hot-melt procedure or by machine sewing. The latter typically forms a stronger joint. With more compact automobiles being designed with small engine compartments and front engine and front drive design, OHC toothed drive belts are commonly subjected to higher temperatures. The hot-melt joining is thus not preferred in that it may not produce a strong enough joint. Thus, for this environment, the belts with machine-sewn joints are more commonly used.
Belts with machine-sewn joints have some potential problems. If the joint is located at the valleys or edges of the teeth, the joint may be stretched, ultimately to the point that the canvas opens up, exposing the underlying rubber and thereby making the belt prone to cracking.
In JP-B Hei-3-18821, one proposed solution to this problem is disclosed. The belt sleeve, from which the individual belts are cut, is produced by inserting a wire into the joint on a cylindrical canvas cloth on the inner surface of the cloth. The cylindrical cloth is then placed around a mold. A cord is then wrapped around the cloth after which the wire is removed. Unvulcanized rubber is applied over the cloth wrapped with the cord, and thereafter vulcanized.
With machine-sewn joints, the strength of the joint may vary, depending on, for example, the toughness of the canvas cloth and the potential change in the feed range (change in the slip ratio), which is affected by the surface condition of the canvas cloth. As a result, the strength may vary, even though all the other conditions remain the same. Sewing that is too strong or too weak may cause failure in the cloth, and ultimately the belt rubber.
For example, if the joint is too strongly sewn, the joint may protrude from the cloth. The protruded joint may embed in the teeth. This location may be the starting point for cracking in relatively early stages of the belt life.
On the other hand, if the joint is weakly sewn, the joint may open up, depending upon its location on the mold. With the joint on the projecting portions of the mold, there is less a tendency to stretch. However, with the joint located in the mold grooves, the joint tends to open under the flow of rubber into the mold. Unvulcanized rubber may bleed through the joint. Early failure of the belt may originate at this location. Additionally, the belt may tend to creak at the joint location as it is wound around a pulley.